INTERACTIVE EFFECTS OF SALINITY, NITROGEN AND SULFUR ON THE ORGANIC SOLUTES IN SPARTINA-ALTERNIFLORA LEAF BLADES

Glycinebetaine, proline, asparagine, sucrose, glucose, and dimethylsul phoniopropionate (DMSP) were the major organic solutes in Spartina alt erniflora leaf blades, To investigate the physiological role(s) of the se solutes, the effects of salinity, nitrogen, and sulphur treatments on leaf blade solute levels were examined, Glycinebetaine was the majo r organic solute accumulated in leaf blades grown at 500 mol m(-3) NaC l, although asparagine and proline also accumulated when the supply of nitrogen was sufficient, These solutes may play a role in osmotic adj ustment, In contrast, DMSP levels either did not change or were reduce d in response to the 500 mol m(-3) NaCl treatment. Furthermore, elevat ed nitrogen supply decreased leaf blade DMSP levels, which was opposit e to the response of glycinebetaine, proline, and asparagine. A 1000-f old increase in external sulphate concentration had no effect on the l eaf blade levels of DMSP, glycinebetaine, proline, or asparagine. Thes e findings suggest that the major physiological role of DMSP in S. alt erniflora leaf blades is not for osmotic adjustment, even under condit ions of nitrogen deficit and excess sulphur, Instead, DMSP which was p resent at 45-130 mu mol g(-1) dry weight, may play a role as a constit utive organic osmoticum.